Process for preparing an aqueous dispersion of a polyacrylate-modified polyurethane-alkyd resin and the use of such a dispersion

A multistage process for preparing an aqueous binder dispersion (BM) comprising an acrylate-modified polyurethane-alkyd resin (A'), the process comprising:

• (I) preparing a polyurethane alkyd resin (A) comprising:
• (a) from 5 to 50% by weight of a mixture comprising:
• (a1) from 90 to 30 parts by weight of an unsaturated C6 to C30 fatty acid having at least two nonconjugated double bonds, and
• (a2) from 10 to 70 parts by weight of an unsaturated C6 to C30 fatty acid having at least two conjugated double bonds,
• as esterified polymer side chains of the polyurethane-alkyd resin component (A), and
• (b) from 95 to 50% by weight of polyurethane units with monomer building blocks having anionic groups and/or groups which can be converted by neutralization into anionic groups, as polymer main chains of the polyurethane-alkyd resin component (A),
• (II) neutralizing the amionic groups and/or groups which can be converted into anionic groups and converting the polyurethane-alkyd resin component (A) into an aqueous dispersion or solution, and
• (III) polymerizing at least one ethylenically unsaturated, free-radically polymerizable monomer (c) which has essentially no reactive functional groups other than the C--C double bond, in the aqueous dispersion or solution of stage (II) in the presence of a free-radical polymerization initiator.